1. Field of the Invention
The present invention generally relates to a continuous process of subjecting polymeric material to a multiple sequential processing system, wherein each processing step of the system operates at different processing conditions to synergistically enhance the pelletization and crystallization of polymer and polymeric formulations, dispersions, and solutions.
2. Description of the Prior Art
The generally independent processes and equipment in the conventional multiple sequential processing system of polymeric material are known, some for many years, and used in various applications. As used herein, the term “multiple sequential processing system” includes the steps, processes and equipment for mixing/extrusion, pelletization, transportation, crystallization, drying, and post-processing manipulations of polymeric material pellets. Yet, the prior art is silent to the controlled and intentional application of these processes in the multiple sequential processing system to synergistically enhance the crystallization of polymeric materials.
Pelletization equipment and its use following extrusion processing have been implemented for many years by the assignee as demonstrated in prior art disclosures including U.S. Pat. Nos. 4,123,207; 4,251,198; 4,500,271; 4,621,996; 4,728,176; 4,888,990; 5,059,103; 5,403,176; 5,624,688; 6,332,765; 6,551,087; 6,793,473; 6,824,371; 6,925,741; 7,033,152; 7,172,397; US Patent Application Publication Nos. 20050220920, 20060165834; German Patents and Applications including DE 32 43 332, DE 37 02 841, DE 87 01 490, DE 196 42 389, DE 196 51 354, DE 296 24 638; World Patent Application Publications WO2006/087179, WO2006/081140, WO2006/087179, and WO2007/064580; and European Patents including EP 1 218 156 and EP 1 582 327. These patents and applications are all owned by the assignee and are included herein by way of reference in their entirety.
Similarly, dryer equipment has been used by the assignee of the present invention for many years as demonstrated in the prior art disclosures including, for example, U.S. Pat. Nos. 3,458,045; 4,218,323; 4,447,325; 4,565,015; 4,896,435; 5,265,347; 5,638,606; 6,138,375; 6,237,244; 6,739,457; 6,807,748; 7,024,794; US Patent Application Publication No. 20060130353; World Patent Application Publication No. WO2006/069022; German Patents and Applications including DE 19 53 741, DE 28 19 443, DE 43 30 078, DE 93 20 744, DE 197 08 988; and European Patents including EP 1 033 545, EP 1 602 888, EP 1 647 788, EP 1 650 516. These patents and applications are all owned by the assignee and are included herein by way of reference in their entirety.
Additionally crystallization processes and equipment are also disclosed by the assignee exemplarily including U.S. Pat. No. 7,157,032; US Patent Application Publication Nos. 20050110182, 20070132134; European Patent Application No. EP 1 684 961; World Patent Application Publication Nos. WO2005/051623 and WO2006/127698. These patents and applications are all owned by the assignee and are included herein by way of reference in their entirety.
Post-processing manipulations as used herein can include thermal manipulation, pellet coating, particle sizing, storage, and packaging of the pellets thusly formed, and are well-known to those skilled in the art.
World Patent Application Publication No. WO/2007/064580 discloses the sequential mixing and/or extrusion processes to provide exceptional control of the temperature, shear, rheology, and subsequent processing conditions facilitating pelletization of high melt index, low viscosity, narrow melting range, polymeric mixtures, formulations, dispersions, or solutions in avoidance of phase separation and die freeze-off, but remains silent as to the importance of, or processes for, crystallization of such materials.
U.S. Pat. No. 2,918,701 discloses the use of water in a cutting chamber that is cool enough to allow the pellet skin to harden quickly to minimize the sticking or jamming of those pellets, yet retain internal heat sufficient for self-drying without being too cool to prevent assumption of the desired shape of the pellet. Water of higher temperatures introduced after the cutting chamber can aid in the drying process. The disclosure remains silent regarding the use of multiple process temperatures and methods to achieve crystallization.
U.S. Patent Application Publication No. 2005/0085620 discloses the use of pelletization wherein the transport water is under pressure. The pellets so produced according to this disclosure and World Patent Application Publication No. WO/2006/128408 are removed from the water, dried, and conveyed to a separate device wherein they are maintained at elevated temperature with agitation to effect crystallization. Similarly, U.S. Patent Application Publication No. 2005/0065318 crystallizes pellets optionally produced by underfluid granulation in a pressurized crystallization chamber at 140° C. with, or preferably without, agitation. Use of a pipe for thermally crystallizing the pellets is disclosed therein.
U.S. Patent Application Publication No. 2005/0062186 discloses a strand granulation device resulting in pellets that are conveyed while hot to a thermal treatment device for solid state crystallization and subsequent polycondensation. An alternate mechanism is disclosed wherein the cooling water for pelletization and the conveyance device are pressurized.
U.S. Pat. No. 7,250,486 discloses the use of a cooling liquid under pressure to solidify granules sufficient for cutting while retaining the bulk temperature of the particle in a range conducive to crystallization. A second warming liquid under pressure replaces the original cooling liquid to maintain this temperature range for crystallization, relying on the exothermic nature of the crystallization process to accelerate the rate of the pellet crystallization. The liquids disclosed are preferably water under pressures ranging from approximately 131 kPa (approximately 19 psig) to approximately 2731 kPa (approximately 136 psig) and may include additives like ethylene glycol to raise the boiling point and potentially lower the effective pressures. Similarly, US Patent Application Publication No. 2005/0167876 discloses a pressurized pelletization process with optional conveyance to a second pressurized vessel for enhancement of crystallization.
U.S. Patent Application Publication No. 2005/0004341 discloses multiple conditioning steps potentially of long, multiple-day duration, prior to crystallization wherein control of the moisture content and/or moisture profile is stressed. Yet, it remains silent as to the continuous and accelerated fluid transport of the pellets between conditioning steps.
World Patent Application Publication No. WO/2000/023497 discloses a multiple step process in which granulation results in a cooled product that is conveyed to a second treatment vessel wherein fluid temperatures are preferably in excess of 100° C. Ethylene glycol and triethylene glycol are preferred alone, in combination, or as additives to the water for maintenance of the temperatures up to 230° C.
U.S. Pat. No. 3,988,085 discloses the use of air injection to facilitate transport of pellets, but remains silent as to an enhancement mechanism for crystallization. The injection of high velocity air or other inert gas into the liquid and pellet slurry line as disclosed in U.S. Pat. No. 7,157,032 increases the speed of the pellets into and through a dryer retaining sufficient heat in the pellets to initiate self-crystallization. Yet, it remains silent as to the use of multiple sequential processing systems for the enhancement of crystallization.
World Patent Application Publication No. WO/2006/127698 similarly discloses the injection of high velocity air to retain sufficient internal heat in pellets for self-initiation of crystallization. It further discloses the use of a pellet crystallization system that optionally and sequentially can be attached to a dryer or to a vibratory unit to provide additional crystallization and cooling for the pellets. It further discloses the enhancement of crystallization effected by the residual latent heat of the pellets and subsequent cooling following drying as facilitated by a 20 second to 120 second retention period of those pellets on a vibratory unit. WO/2006/127698 remains silent as to the use and benefits of differing temperatures in the sequential processing systems as well as the duration of time achieved by the pellet crystallization system for the synergistic enhancement of that crystallization.
What is needed, therefore, is a multiple sequential processing system to facilitate the thermal, shear, and Theological control of pelletization, and to enhance crystallization of pellets formed. Each of the processes/steps of such a multiple sequential processing system is operated at certain processing conditions (for example, temperature, pressure, flow rate, residence time, and transfer agent), and a beneficial multiple sequential processing system would utilize processes/steps wherein no two processes/steps of the system would utilize an equivalent set of processing conditions. For example, a beneficial system would utilize processes/steps that each differ from another in at least one processing condition, for example, operational temperature ranges, and wherein crystallization processes/steps preferably are not at temperatures in excess of the boiling point of water. Transfer between the sequential processes of the system is optionally expedited to retain the internal heat of the pellets, and residence time in each process of the system is specific to a particular material providing the maximum synergistic crystallization for that material wherein introduction of additional pressure and/or additives to achieve higher boiling points and the associated safety hazards therewith are preferably not essential to enhance crystallization of the pellets. It is to such a method that the present invention is primarily directed.